1. Field of the Invention
This invention relates to a film advance device of a camera, and more particularly to a device for restraining any further film advance upon completion of the film advance of one frame and releasing the restraint upon termination of exposure.
2. Description of the Prior Art
A film advance device is designed such that when film has been advanced by one frame and/or when shutter charge has been completed, a film advance mechanism is restrained so that any further film advance does not take place. Usually, this restraint of film advance is accomplished by holding a member operatively associated with a film advance shaft by a restraining lever and, immediately after completion of the exposure of film, the lever is moved to thereby release the restraint.
However, in recent years, along with the increased use of the electric driving device of a camera, development of a technique for increasing the number of frames photographed per unit of time has been desired. In view of such desire, starting the aforementioned restraint releasing operation while waiting for the completion of the exposure of film as has heretofore been done would cause a time delay and this is disadvantageous.
On the other hand, the time when a film advance signal is produced for the electric driving device may likewise be considered as follows. That is, in the past, the film advance signal for the electric driving device has been produced by completion of the movement of the rearward shutter curtain or, in a single lens reflex camera, by the operation of the mirror mechanism returned thereby, to start film advance.
In this system, however, the mechanical delay resulting from the inertia of the electric driving device during the actuation thereof cannot be neglected and film advance is not started in spite of the camera side having become ready to effect the next film advance, and this has meant a waste of time and it has been impossible to increase the number of frames photographed per unit of time.
Such tendency has been more pronounced in cameras of the type in which the electric driving device is operatively associated with the mirror mechanism, because the time for starting film advance is more delayed therein.